Lithium secondary batteries are being widely used in various types of portable electronic devices including personal computers, camcorders, mobile phones, portable CD players, and personal digital assistants (PDAs), due to having many advantages of high energy density and high operating voltage as well as excellent storage and life characteristics.
Generally, a lithium secondary battery includes a cylindrical or prismatic case, an electrolyte, and an electrode assembly received in the case. Here, the electrode assembly includes a stack of a cathode, separator, and an anode, and has a jelly-roll type wind structure or a stack structure.
The electrode assembly composed of cathode/separator/anode may have merely a stack structure, but may have a structure in which a plurality of electrodes (cathodes and anodes) are stacked with a separator interposed therebetween and joined with each other by heat/pressure. In this case, the joining of the electrode and the separator is achieved by applying heat/pressure with an adhesion layer coated on the separator and the electrode facing each other. Here, the separator is generally made by an extrusion molding process using a polyolefine resin as a raw material, and to improve the properties including the adhesive strength with the electrode, a material such as a binder or the like may be coated thereon.
Conventionally, a gel polymer coating technique, an electrospinning technique, or the like, was used to coat the binder material on the separator.
However, these exemplary coating techniques involve coating the binder material over the entire separator surface, which hinders the transport of lithium ions. That is, as the coating layer of the binder material formed on the separator is adhered to the electrode where lithium ions transfer, the coating layer is a factor discouraging the lithium ion transfer.